Is unctuousness always obvious?

Hi, I have a quick question about the word unctuous that would better help me to more accurately use the word. I see that it is used to describe behavior or speech marked by false sincerity. An unctuous person uses flattery, compliments, kindness and other psychological tactics to become more likable to their target in order to become more influential and thus get what they want.

Now, it is possible to be insincere in a way that is not obvious. One could trick others into truly believing that the compliment or kindness is genuine. But I'm not sure if the word unctuous can be used to describe such "non-obvious" kindness or compliments..?

So my question is whether unctuousness always implies obviousness of false sincerity..? Or can unctuous behavior also be more obscured and not so obvious?

Looking forward to a better understanding of this word. Thank you!